1. Field
A method of preparing a lithium secondary battery is disclosed.
2. Description of the Related Art
A non-aqueous lithium secondary battery typically includes a separator made of a porous insulating film and interposed between positive and negative electrodes. The pores of the film are impregnated by an electrolyte solution including a lithium salt dissolved therein. The non-aqueous lithium secondary battery has excellent initial high-capacity and high energy density characteristics.
However, when the positive and negative electrodes therein are repetitively contracted and expanded during the charge and discharge cycles, they react with the separator or the electrolyte, and, as a result, the non-aqueous lithium secondary battery may be easily deteriorated, which may result in internal and external short circuits and rapid increases in the temperature of the battery. When the temperature of the battery rapidly increases, the separator fuses and is rapidly contracted or destroyed and, thus, can be short-circuited.
In order to prevent this problem, a separator is formed of a porous polyethylene film having excellent shutdown characteristic, easy handling, and low cost. Herein, the shutdown characteristic causes the separator to become partly fused, thereby closing pores and cutting off the current, when the temperature of the battery increase due to overcharge, external or internal short circuit, or the like.
In addition, attempts have been made to improve safety of the non-aqueous lithium secondary battery by improving heat resistance of the electrode material, the separator, and the like, and in particular, to secure safety even when the separator is sharply contracted or destroyed.